The present invention relates to an improved process for forming non-cyclic, aliphatic compounds having a multiplicity of primary amino groups and forming these compounds in high yields and selectivity from the corresponding polynitrile having from 2 to 3 atoms between the cyano groups.
The hydrogenation of nitriles to amines using conventional hydrogenation catalysts is well known. However, it is recognized that this synthetic mode is not an effective process for forming noncyclic, aliphatic compounds from polynitrile having an atomic structure capable of forming five and six membered ring containing compounds. In such cases the presently known hydrogenation processes provide noncyclic products in low selectivity and yield. This is especially true with polynitriles such as nitrilotriacetonitrile, iminodiacetonitrile and ethylenediaminetetraacetonitrile. Normally, the dominant products formed are cyclic polyamines. When one attempts to adjust the reaction conditions to those which may provide higher selectivity or yield of the non cyclic, aliphatic compound, one observes rapid inactivation of the catalyst materials used.
It is generally known that hydrogenation of nitriles can be accomplished by many modes such as by a batch process using an autoclave or by continuous process using a fixed bed reactor to contact a hydrogenation catalyst with a solution containing a nitrile. The reaction product is generally a mixture of primary, secondary and tertiary amines. The formation of the later two amines are thought to be due to the reaction of an imine intermediate with some of the primary amine product present in the reaction zone to produce a secondary amine, and in turn, the reaction of the imine with some of the secondary amine to form a tertiary amine product. When the starting nitrile has a multiplicity of cyano groups which are separated by an appropriate chain length of about 2 to 3 atoms, the secondary and tertiary amine formation tends to be intramolecular to provide cyclic compounds as the dominate product. Thus, when a dinitrile, such as iminodiacetonitrile, is subjected to conventional hydrogenation, one forms the cyclic compound, piperazine, as the major material. For a trinitrile, such as nitrilotriacetonitrile, the difficulty of forming the corresponding linear aliphatic amine, tris(2-aminoethyl) amine, increases geometrically. Thus, contacting of a polynitrile with a hydrogenation catalyst is a recognized route for producing cyclic polyamines.
U.S. Pat. Nos. 3,565,957 and 3,733,325 teach that the yields of the cyclic amine can be optimized by carrying out the reaction in the presence of large amounts of ammonia. By using a hydrogenation catalyst in the absence of ammonia to increase the yield of linear product, one produces a solid material which inactivates the catalyst in a very short period of time. The short life of the catalyst as well as low selectivity and yield has caused this process to be deemed economically unfeasible in commercially providing linear polyamines.
In all of the hydrogenation processes that are used in converting polynitriles to polyamines one requires using a solution of the initial polynitrile in an inert solvent. Materials which are known to be useful as inert solvents are alcohols, amides, and ethers as they do not interact with the other materials in the reaction zone to detract from the overall yield and selectivity of the products being formed. When the product desired is a cyclic amine, ammonia has, in certain instances, been utilized as a solvent or cosolvent for the process. It has been thought that due to the reactivity of the imine intermediate product with amine groups one should not utilize amine materials as the solvent in such processes as they would tend to interact with the imine to form a condensation reaction product and detract from the overall selectivity of the desired materials.
It is highly desired to find an economically feasible process for forming, in high selectivity and yield, non-cyclic aliphatic polyamines from corresponding polynitriles. The formed linear polyamines have known usefulness as chelating and sequestering agents and as reagents in the formation and crosslinking of polymeric products, such as polyurethanes and the like.